The present invention relates to means for reducing or eliminating the internal bypassing of gas streams around the heating elements in rotary regenerative heat exchangers and particularly relates to the internal bypassing of air and flue gas streams around the heating elements in an air preheater.
In a rotary regenerative air preheater, the rotor is divided up into pie-shaped sectors, which are in turn subdivided into rotor compartments. Each rotor compartment is designed to accommodate one or more assemblies of heating elements comprising basket-like containers and heat transfer surfaces therein. Because of fabrication tolerances and/or the distortion of the rotor structure associated with extended operation under varying thermal conditions, it is usually necessary to design the heating elements to allow a clearance around each basket so as to avoid interference at installation.
When fabrication tolerances, rotor distortion and/or design clearances result in excessive gaps ("bypass gaps") between the sides of the basket and the corresponding side wall of the rotor compartment or adjacent basket, a portion of the air and gas streams will flow through the gaps thereby bypassing the heat transfer surfaces and thereby resulting in a loss in heat transfer efficiency.
Bypass gaps have been addressed in the past by a practice known as "tabbing" which entailed the welding of bypass strips over gaps deemed large enough to close, or with resilient sealing devices installed in gap areas large enough to accept them. Both of these approaches are costly in field labor expense and/or material. Generally, every layer of heating elements needs to be tabbed or sealed individually.